Auto-signing fails since update to a new MacBook Pro

I updated my MacBook to a more recent one. So I exported my developer keys and profiles on the old MacBook (Mojave) and re-imported them into the new machine (Catalina). The rest of the setup is identical, i.e. same version of Unity and same version of Xcode.

Whenever I create a new iOS build from Unity, something strange happens: Although automatic signing is enabled, Xcode complains that the team is unknown, so the build fails. Only if I manually select the team again, everything works as expected. For the next build, the procedure restarts.

So I am wondering how Unity sets up the signing process and how I can prevent it from breaking the signature flow. I did not experience these problems on the old MacBook.